1. Field of the Invention
The present invention relates generally to sealing gaskets used for pipe joints in which a male spigot pipe section is installed within a mating female socket pipe section and, more specifically, to an improved gasket and installation method for installing a locked-in gasket within a preformed gasket groove in a section of pipe used to form a pipe joint. 2. Description of the Prior Art
Pipes formed from thermoplastic materials including polyethylene, polypropylene and polyvinyl chloride are used in a variety of industries. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. It is critical, during the installation process, that the gasket not be able to twist or flip since a displaced or dislocated gasket will adversely affect the ultimate sealing capacity of the joint.
One early attempt to ensure the integrity of pipe joints used under demanding conditions was to provide local reinforcement of the groove portion of the female socket end by means of a heavier wall thickness in this region of the pipe. In some cases, reinforcing sleeves were also utilized. Each of these solutions was less than ideal, in some cases failing to provide the needed joint integrity and often contributing to the complexity and expense of the manufacturing operation.
In several of the prior art commercial systems using pipes with preformed grooves, the sealing gaskets were provided in two parts. The main gasket body was formed of an elastomeric material and typically featured an internal groove or recess. A hardened band, formed of rigid plastic or metal, was installed within the groove. While such retaining bands helped to resist axial forces acting on the gasket during assembly of the joint, the band could become displaced or twisted during the insertion operation.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system employed a unique pipe belling operation which seated the sealing gasket during belling. In the Rieber process, an elastomeric gasket was installed within an internal groove in the socket end of the female pipe as the female or belling end was simultaneously being formed by forcing the belling end over a forming mandrel. Rather than utilizing a preformed groove, the Rieber process provided a prestressed and anchored elastomeric gasket during the belling operation. Because the pipe groove was, in a sense, formed around the gasket, the gasket was securely retained in position and did not tend to twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
Despite the advances offered by the Rieber process, the belling operation was somewhat complicated and costly. Also, certain situations exist in which it would be desirable to install a gasket within a preformed groove in the selected pipe end, rather than utilizing an integrally installed gasket in which the groove in the pipe is formed around the gasket.
The present invention has, as one object, to provide an improved pipe gasket for use in pipe joints which offers the advantage of a Rieber type locked-in seal while allowing the gasket to be installed in a preformed groove.
Another object of the invention is to provide an improved gasket which is securely retained within a preformed pipe groove without the necessity of a separate retaining band.
Another object of the invention is to provide a design formula for precisely locating an internal retaining ring within the elastomeric body of a sealing gasket which is thereafter inserted in a preformed pipe groove.
Another object of the invention is to provide a method for installing a gasket having a known external diameter and having an internal retainer ring within the mouth opening of a bell end of a pipe section where the external diameter of the gasket exceeds the nominal internal diameter of the mouth opening and where the location of the retainer ring is predetermined to facilitate the insertion process.